System and method for controlling solenoid pressure

ABSTRACT

A method for calibrating an input electrical signal to an individual pressure control device includes the steps of providing a target pressure-to-current (P/I) threshold, providing a lower estimated P/I threshold, and providing an estimated P/I curve that passes between the target P/I threshold and the lower estimated P/I threshold. Next, the method determines a lower actual P/I threshold at a pressure equal to the pressure at the lower estimated P/I threshold. A maximum offset current is calculated from the difference between the currents at the lower actual P/I threshold and the lower estimated P/I threshold. Finally, the method calculates a calibrated P/I curve. The calibrated P/I curve includes the target P/I threshold and the lower actual P/I threshold. The slope of the calibrated P/I curve is calculated as a proportional value of the maximum offset current.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/051,780, filed on May 9, 2008. The disclosure of the aboveapplication is incorporated herein by reference.

FIELD

The present disclosure relates to a system and method for controllingsolenoid pressure, and more particularly to a system and method forcompensating for the pressure output differences between solenoids in acontrol system.

BACKGROUND

The statements in this section merely provide background informationrelated to the present disclosure and may or may not constitute priorart.

Electro-hydraulic pressure control devices (for example, a VariableBleed Solenoid (VBS) or related device) are used to control automotiveautomatic transmissions and other systems. These electro-hydraulicpressure devices provide an output pressure that is a function of anelectrical input. The electrical input is typically controlled andprovided by a microprocessor based controller. The output pressure inturn is used to control components within the transmission. For example,a typical automatic transmission includes a plurality of actuatablefriction devices, such as clutches or brakes that are controlled by anelectronic control system. The electronic control system must providethe desired clutch pressure as prompted by an electrical input signal inorder to achieve acceptable shift quality. Variations or inaccuracies inthe output pressure supplied by the electro-hydraulic pressure devicecan decrease the shift quality of the transmission. Electro-hydraulicpressure device manufacturers have struggled to minimize thesevariations and inaccuracies.

One solution to variations and inaccuracies in the actual outputpressure supplied by the electro-hydraulic pressure device is to adjustor calibrate the device in a final production test phase. However, knownmethods of calibrating the electro-hydraulic pressure device adjustmentthe curve that defines the relationship between input current and outputpressure along the electrical input axis and does not significantlyalter the overall curve shape or slope. While this adjustment is veryhelpful, it often is unable to prevent high electro-hydraulic pressuredevice reject rates at the supplier and does not address variationbetween individual devices in curve slope over the operating range.

Accordingly, there is a need in the art for a method of automaticallycalibrating a electro-hydraulic pressure device that improves on theaccuracy of the calibration process. Additionally, this method shouldnot require additional hardware components.

SUMMARY

The present invention provides a method for calibrating an inputelectrical signal to an individual pressure control device. The methodincludes the steps of providing a target pressure-to-current (P/I)threshold, providing a lower estimated P/I threshold, and providing anestimated P/I curve that passes between the target P/I threshold and thelower estimated P/I threshold. Next, the method determines a loweractual P/I threshold at a pressure equal to the pressure at the lowerestimated P/I threshold. A maximum offset current is calculated from thedifference between the currents at the lower actual P/I threshold andthe lower estimated P/I threshold. Finally, the method calculates acalibrated P/I curve. The calibrated P/I curve includes the target P/Ithreshold and the lower actual P/I threshold. The slope of thecalibrated P/I curve is calculated as a proportional value of themaximum offset current.

Further areas of applicability will become apparent from the descriptionprovided herein. It should be understood that the description andspecific examples are intended for purposes of illustration only and arenot intended to limit the scope of the present disclosure.

DRAWINGS

The drawings described herein are for illustration purposes only and arenot intended to limit the scope of the present disclosure in any way.

FIG. 1 is a schematic diagram of a system and method of calibrating apressure control device according to the principles of the presentinvention; and

FIG. 2 is a graph illustrating the method of calibrating a pressurecontrol device according to the principles of the present invention.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is notintended to limit the present disclosure, application, or uses.

With reference to FIG. 1, a system for calibrating a pressure controldevice is generally indicated by reference number 10. The system 10generally includes a temperature sensor 12, a pressure control device14, and a controller 16. The system 10 in the embodiment provided isemployed in a transmission of a motor vehicle. However, it should beappreciated that the system 10 may be employed in various otherembodiments that use pressure control devices, such as, for example,engines or control systems.

The temperature sensor 12 is operable to detect or sense the currentoperating temperature of the transmission. The temperature sensor 12 maytake various forms without departing from the scope of the presentinvention. The pressure control device 14 is a valve or solenoid that isoperable to provide an output pressure in response to an electricalinput signal. In the embodiment provided, the pressure control device 14is a variable bleed solenoid that is operable to provide variable outputpressure. Accordingly, the amount of output pressure is a function ofthe input electrical signal received by the pressure control device 14.It should be appreciated, however, that the pressure control device 14may take various other forms without departing from the scope of thepresent invention. In the example provided, the pressure control device14 is one of a plurality of pressure control devices that are part of ahydraulic control system. The output pressure provided by the pressurecontrol device 14 is operable to control actuation or engagement of atleast one of a plurality of torque transmitting devices, such asclutches and brakes.

The controller 16 is, in the example provided, a transmission controlmodule having a preprogrammed digital computer or processor, controllogic or routines, memory used to store data, and at least one I/Operipheral. However, other types of controllers may be employed withoutdeparting from the scope of the present invention. The controller 16 isin communication with the temperature sensor 12 and with the pressurecontrol device 14. More specifically, the controller 16 is configured toreceive data signals from the temperature sensor 12 indicative of theoperating temperature of the transmission and to send control signals orinput electrical signals to the pressure control device 14. The inputelectrical signals are preferably in the form of a controlled directcurrent or a voltage pulse width modulation duty cycle percent.

During operation of the transmission, the controller 16 includes clutchcontrol logic 20 that determines which torque transmitting devices mustbe engaged or disengaged at any given time. The clutch control logic 20generates a clutch pressure request 22 that is indicative of therequired hydraulic fluid pressure needed to engage or disengage thetorque transmitting devices. The clutch pressure request 22 is thenfiltered through a temperature compensating pressure-to-signal look-uptable 24. The controller 16 uses the current operating temperature ofthe transmission as sensed by the temperature sensor 12 to adjust theclutch pressure request signal to account for the temperature. Morespecifically, the temperature compensating pressure-to-signal look-uptable 24 provides an input signal required to produce the requestedoutput pressure calibrated for transmission temperature.

With reference to FIG. 2, the controller 16 stores in memory a nominalpressure-current (P/I) curve 30 that estimates the relationship betweenan input signal, such as, for example, an electrical current, and anactual output pressure provided by the pressure control device 14. Itshould be appreciated that the pressure scale shown in FIG. 2 can referto either output pressure directly measured from the pressure controldevice 14 or clutch pressure. The nominal curve 30 has a calibrationtarget threshold 32 located near an upper region (high pressure and highcurrent) of the nominal P/I curve 30. The calibration target threshold32 is selected to be near the upper end of the transmission's criticalclutch control pressure range (i.e. the upper range of output pressuresthat are critical to accurately controlling the clutch or other devicethat receives the output pressure). The pressure control device 14 ismanufactured to have an actual P/I curve that passes through thecalibration target threshold 32. Accordingly, at the calibration targetthreshold 32 the estimated current required to provide an actual outputpressure from the pressure control device 14 is equal to the actualcurrent required to provide the actual output pressure. However, theactual P/I curve for the pressure control device 14 (i.e., the actualcurrent needed to supply a given actual output pressure) may vary fromthe nominal P/I curve above and below the calibration target threshold32.

In order to account for this difference between the actual P/I curve andthe nominal P/I curve, the controller 16 initiates a method forcalibrating the input signal in order to accurately provide a desiredoutput pressure supplied by the pressure control device 14. The methodincludes a lower calibration threshold routine 26 and a proportionaloffset routine 28. The lower calibration threshold routine 26establishes a lower calibration threshold 34. The lower calibrationthreshold 34 is the actual current required to produce a given outputpressure. The lower calibration threshold 34 has the same outputpressure as a lower nominal threshold 36 located on the nominal P/Icurve 30. However, due to the individual operating characteristics ofeach pressure control device 14 noted above, the actual current at thelower calibration threshold 34 is different from the estimated currentat the lower nominal threshold 36. The lower calibration threshold 34 isautomatically established for each pressure control device 14 in thetransmission during transmission operation by the lower calibrationthreshold routine 26. One method of establishing the lower calibrationthreshold 34 includes optimizing diagnostic system hardware to determinethe actual current required to achieve a specific output pressure fromeach pressure control device 14 in the transmission. This method isdescribed in commonly assigned U.S. Pat. No. 6,382,248, hereinincorporated by reference as if fully disclosed herein. Another methodof establishing the lower calibration threshold 34 includes usingsoftware that is operating while the running vehicle is still on theassembly line to determine the actual current that each pressure controldevice 14 requires to begin clutch engagement. This method is describedin commonly assigned U.S. Pat. No. 7,069,767, herein incorporated byreference as if fully disclosed herein. The lower calibration threshold34 is selected to be at the lower end of the transmission's criticalclutch control pressure range, i.e., the range of clutch or pressurecontrol device output pressures that can significantly affect shiftquality. The lower calibration threshold 34 is obtained when thetransmission is at a temperature consistent with the temperature sensedby the temperature sensor 12 and used by the temperature compensatingpressure-to-signal look-up table 24. Accordingly, the controller 16 mayprovide an interim lower calibration threshold 34 value from non-targettemperature data while amassing target temperature data for the finallower calibration threshold 34 value.

Next, the proportional offset routine 28 within the controller 16calculates an offset signal or current from the difference between theactual current determined by the proportional offset routine at thelower calibration threshold 34 and the estimated current at the lowernominal threshold 36 for the same output pressure. The offset current isthen used to create a calibrated P/I curve or relationship 38 thatincludes both the calibration target threshold 32 and the lowercalibration threshold 34. The offset current used to calculate thecalibrated P/I curve between the calibration target threshold 32 and thelower calibration threshold 34 is proportional to the requested outputpressure between the thresholds 32 and 34. In other words, the offsetcurrent for a given output pressure varies non-linearly betweenthresholds 32 and 34 based on what output pressure is requested.Accordingly, the maximum current offset occurs when an output pressureis required at the lower calibration threshold 34. The offset currentrequired for output pressures between the lower calibration threshold 34and the target threshold 32 then decreases non-linearly as the outputpressures approach the target threshold 32. At all output pressurerequests located between thresholds 32 and 34 on the P/I curve, theoffset current would be proportional to the location of the requestedpressure between the pressures of thresholds 32 and 34. At all outputpressure requests below threshold 34, the offset current used is theoffset current measured between the lower calibration threshold 34 andthe lower nominal threshold 36. If an output pressure at or above thecalibration target threshold 32 is requested, no modification of thecurrent is required. Accordingly, the proportional offset routine 28 isoperable to determine a calibrated current command 40 from the clutchpressure request.

The calibrated current command 40 is then communicated to a devicedriver 42, which in turn is operable to send a control signal to thepressure control device 14. The control signal more closely matches theP/I characteristics of each pressure control device 14 in thetransmission.

The description of the invention is merely exemplary in nature andvariations that do not depart from the gist of the invention areintended to be within the scope of the invention. Such variations arenot to be regarded as a departure from the spirit and scope of theinvention.

1. A method for calibrating an input signal sent to a pressure control device with an output pressure provided by the pressure control device, the method comprising the steps of: providing a target threshold that comprises a first actual input signal operable to produce a first output pressure; providing a lower estimated threshold that comprises a first estimated input signal estimated to produce a second output pressure; providing an estimated signal-to-pressure relationship that provides a plurality of estimated input signals estimated to produce a plurality of output pressures, the estimated signal-to-pressure relationship including the target threshold and the lower estimated threshold; determining a lower target threshold that comprises a second actual input signal required to produce the second output pressure; calculating a signal offset from the difference between the second actual input signal and the first estimated input signal; determining a calibrated signal-to-pressure relationship that provides a plurality of calibrated input signals operable to produce the plurality of output pressures, wherein the plurality of calibrated input signals are proportionally offset from the plurality of estimated input signals using a proportional value of the signal offset.
 2. The method of claim 1 wherein the target threshold is located in an upper range of output pressures provided by the pressure control device.
 3. The method of claim 1 wherein the lower estimated threshold is located in a lower range of output pressures provided by the pressure control device.
 4. The method of claim 1 wherein the plurality of output pressures is located between the first output pressure and the second output pressure.
 5. The method of claim 1 wherein the signal offset used to calculate each of the plurality of calibrated input signals decreases as the pressure increases between the first output pressure and the second output pressure.
 6. The method of claim 1 wherein the first output pressure is greater than the second output pressure.
 7. The method of claim 1 wherein the calibrated signal-to-pressure relationship provides a second plurality of calibrated input signals for a second plurality of output pressures that are lower than the second output pressure, and wherein the second plurality of calibrated input signals are offset from the plurality of estimated input signals using the signal offset.
 8. The method of claim 1 further comprising a step of adjusting the calibrated input signals for temperature.
 9. A system for operating a device in a transmission using hydraulic fluid, the system comprising: a temperature sensor for sensing a temperature of the hydraulic fluid within the transmission; a pressure control device for controlling an output pressure of the hydraulic fluid to the device; a controller in communication with the temperature sensor and the pressure control device, the controller having control logic including a first control logic for determining whether the device should be activated, a second control logic for generating a requested output pressure required to activate the device, a third control logic for receiving a signal from the temperature sensor indicative of the temperature of the hydraulic fluid, a fourth control logic for providing an estimated input signal to provide the requested output pressure from the pressure control device that is adjusted for the temperature of the hydraulic fluid, a fifth control logic for providing a target threshold that comprises a first actual input signal operable to produce a first output pressure, a sixth control logic for providing a lower estimated threshold that comprises a first estimated input signal estimated to produce a second output pressure, a seventh control logic for providing an estimated signal-to-pressure relationship that provides a plurality of estimated input signals estimated to produce a plurality of output pressures, the estimated signal-to-pressure relationship including the target threshold and the lower estimated threshold, an eighth control logic for determining a lower target threshold that comprises a second actual input signal required to produce the second output pressure, a ninth control logic for calculating a signal offset from the difference between the second actual input signal and the first estimated input signal, a tenth control logic for determining a calibrated signal-to-pressure relationship that provides a plurality of calibrated input signals operable to produce the plurality of output pressures, wherein the plurality of calibrated input signals are proportionally offset from the plurality of estimated input signals using a proportional value of the signal offset, and an eleventh control logic for using the calibrated signal-to-pressure relationship to determine a calibrated input signal required to produce the requested output pressure.
 10. The system of claim 9 wherein the controller further includes control logic for communicating the calibrated input signal to the pressure control device. 